1. Field of the Invention
The present invention relates to a signal evaluation method for evaluating a signal reproduced from an information recording medium, an information recording/reproducing apparatus, and an information recording medium. More specifically, the present invention is directed to improvements in evaluation means and an evaluation method which reproduce a signal from the information recording medium and evaluates the reproduced signal.
2. Description of the Related Art
As signal processing performed by an information recording/reproducing apparatus, a PRML (partial response and maximum likelihood) discrimination method is known in the art.
Jpn. Pat. Appln. KOKAI Publication No. 2002-358738 discloses a technique for evaluating the signal quality in a system using the PRML discrimination method.
According to the technique of the KOKAI publication, a differential metric distribution is prepared. Based on the assumption that the differential metric distribution is a normal distribution, a standard deviation σ and a mean value μ are obtained. Of the portions of the normal distribution, the portion whose peak is not more than 0 is detected, and an area (error rate) of the detected portion is calculated from the standard deviation σ and the mean value μ, using an error function.
The normal distribution is not necessarily accurate. In practice, a plurality of different normal distributions are superposed. This being so, the error rate cannot be accurately estimated, and the signal quality cannot be evaluated.